"We feel like we're letting our son down by not finding him. He's still out there somewhere; all we want is to bring him home, so he's back with the people who love him, not lying alone somewhere in a cold, unmarked grave."

"Over the last years we have written to Mr Martin in prison, but have never had a reply from him."

"I have spent hours walking the streets and Redways of Milton Keynes looking for Jonathan but it's impossible to cover everywhere. In the early days I would force myself to complete everyday tasks like make a cup of tea and then I would stop and think, 'I shouldn't be doing this, I should be out looking for our son', and those feelings are still with us today."

Detective Chief Inspector Peter Vigurs, from Thames Valley Police, wrote to Martin twice following his release from prison and - like the Dolton family - didn't get a response:

"The message you've heard from the Dolton family is very powerful and yet, even then, it's still hard to imagine exactly how they must feel. What we do know is that we need to find Jonathan's body."

"I believe that Stewart Martin will have told someone what he did with Jonathan's body. So if you are that person, or if you know who that person may be, then I would ask you please come forward, please contact the police and please help us find Jonathan for the sake of his family."

"It doesn't matter if you haven't come forward before. And there's no longer any need to fear or protect Stewart Martin. What matters now is that we find Jonathan for the sake of the family."

Chief Inspector Vigurs told Heart why Martin may not have been willing to give up the information about where he'd put Mr Dolton's body:

"It's very difficult to know and I can only speculate, and all I can think is he felt he would be at risk if the body was found in some way."

Anyone with information can contact Milton Keynes police station on 0845 8 505 505 and quote URN 233 30/11. Or you can call Crimestoppers anonymously on 0800 555 111.